<?php
function buildRandomString($type = 1,$length = 4){
	 if($type==1){
	 	$chars = join("", range(0, 9));
	 }elseif ($type == 2){
	 	$chars = join("", array_merge(range("a", "z"),range("A", "Z")));
	 }elseif($type == 3){
	 	$chars = join("", array_merge(range("0", "9"),range("a", "z"),range("A", "Z")));
	 }
	if($length>strlen($chars)){
		exit("字符串长度不够");
	}
	$chars = str_shuffle($chars);
	return substr($chars,0,$length);
}

?>